Project Summary This new investigator proposal describes a five-year training program for the development of a physician- scientist career studying traumatic brain injury (TBI). This investigator completed a Ph.D. in neurobiology focused on mechanisms and neuroinflammatory responses to diffuse axonal injury (DAI). This investigator completed neurosurgery residency, two fellowships in pediatric neurosurgery and pediatric spinal deformity, and is currently a Clinical Instructor at the University of Pennsylvania. In carrying out the proposed research, the principle investigator will acquire expertise in protein biochemistry, knockout genomics, behavioral studies, and advanced neuroimaging techniques. Dr. Douglas Smith, Professor and Chair of Research in the Department of Neurosurgery, will mentor the principle investigator's scientific development. An advisory committee of outstanding, nationally recognized scientists will provide scientific and career advice. The Department of Neurosurgery at the University of Pennsylvania is committed to providing an ideal setting and resources to ensure the principle investigator's success. The research proposal and environment will allow the principle investigator to develop an academic career and become a leader in the neurotrauma community. Research will focus on the selective vulnerability of unmyelinated axon segments to initiating mechanisms of diffuse TBI as well as treatment strategies to overcome DAI pathobiology. DAI pathogenesis proceeds through a cascade of events leading to delayed or secondary axotomy. This creates a therapeutic window during which treatments may mitigate or prevent axon disconnection. Mechanisms of DAI cytoskeletal injury remain poorly understood and there are no treatments. The proposal seeks to determine precise DAI initiating loci, explain the cytoskeletal protein spectrin's role in axonal injury, and investigate two neuroprotective paradigms to mitigate DAI pathobiology. Using an experimental diffuse TBI murine model, the Specific Aims include: 1.) Determine if the axon initial segment and/or nodes of Ranvier are sites of secondary axotomy following diffuse TBI and 2.) Determine spectrin-mediated contributions to secondary axotomy following diffuse TBI. This proposal will be the first to test the hypothesis that disruption of the spectrin cytosketeton at excitable domains along the axon serves as a nidus for injury. Neuroprotective paradigms include preservation of the spectrin cytoskeleton through exogenous and endogenous inhibition of the protease calpain, which targets spectrin for degradation. The proposed research will improve our understanding of DAI-mediated cytoskeletal injury and test neuroprotective strategies designed to prevent secondary axotomy. The integration of histology, behavioral outcomes, and advanced neuroimaging techniques will create a model that predicts injury severity and prognosticates recovery after diffuse brain injury.